Electrodes for liquid crystal display device

ABSTRACT

In a liquid crystal display device, gases, and in particular, H2 and O2 may be generated. Deleterious effects are avoided by incorporating in at least one of the electrodes a catalyst for the recombination of said gases.

JDU'JJO OK V I v w I L United State 7 r 111 3,748,017 Yamamura et al.[451 July 24, 1973 1541 ELECTRODES FOR LlQUlDCRYSTAL 3,000,000, 11/1911c1111111111=1 al. 350/100 DISPLAY DEVICE 3,614,210 10/1971 Caplan350/278 [76] Inventors: Katsumi Yamamura, 553l-28,

Nakasu, Suwa-shi, Nagano-ken;

Koujl Kakizawa, 780-3, Oaza-Shiga, u Suwwshi. Naganmken; Yoshi,He1lme1er et al.. Further Stud1es of the Dynamlc Scattering Mode inNeumatic Liquid Crystals", IEEE gagging:2231; 52 Trans. on ElectronDevices, ED-l7, pp. 22-26, Jan., Kanemitsu Kubota, 855-4, Shiga, I970Suwa-shi, Nagano-ken; lzuhilro Nishimura, 3-3-5, Owa, Suwa-shi,-

OTHER PUBLICATIONS l'leilmeier et 211.: Dynamic Scattering: A NewElectrooptic Effect in Certain Classes of Nematic Liquid Nagamke! JapanCrystals, Proc. IEEE, vol. 56, pp. 1162-1171, July,

221 Filed: May 26, 1971 1908. I

21 Appl. No.: 146,946

Primary Examiner-Edward S. Bauer [30] Foreign Application Priority DataAttorney -Blum, Moseovitz, Friedman and Kaplan- June 5, 1970 Japan45/48051 June 10, 1970 Japan 45/49489 57' ABSTRACT [52] US. Cl. 350/160LC [51] Int. Cl. G021 1/16 I a li id ry tal display device, gases, andin pani '[58] FlQld of Search 350/160 LC la H and 0 may be gene atuiDelete ious effects are avoided by incorporating in at least one of theelec- Rekrfllces Cited trodes a catalyst for the recombination of saidgases.

UNITED STATES PATENTS 3,505,804 4/1970 Hofstein 58/23 6 Claims, 3Drawing Figures ELECTRODES FOR LIQUID CRYSTAL DISPLAY DEVICE BACKGROUNDOF THE INVENTION Liquid crystal display devices are known in which theliquid crystals are caused to disperse or scatter light by theimposition of an electric field.

Although nematic and cholesteric liquid crystals both scatter light whensubjected to an electric field, the nematic type is particularlysensitive.

Such display devices are both useful and attractive, and would, nodoubt, be widely used if it were not for the fact that the life of suchdevices is relatively short. The difficulty stems from the fact that itis very difficult to free the liquid crystals from traces of water inthe process of manufacture. As a result, when voltage is applied acrossthe crystals, some faradaic current flows and the water is electrolyzedproducing H and 0,. The standard conductive, transparent film used forimposi tion of the electric field consists of tin oxide. The tin oxideis sensitive to reduction by the hydrogen produced in the electrolysisso that the tin oxide gradually darkens and loses its transparency, thusterminating the usefulness of the display device. Furthermore, as thegases are generated, they form bubbles which tend to cling to theinterior surfaces of the vessel containing the liquid crystals, thusinterfering with the effectiveness of the display even without reducingthe tin oxide.

SUMMARY OF THE INVENTION The gases generated in liquid crystal displaydevices as the result of the imposition of an electric field betweenelectrodes in contact with the liquid crystals may be catalyticallyrecombined. To effect the recombination, a catalyst is incorporated inat least one of the electrodes. Suitable catalysts for the recombinationof hydrogen and oxygen are the transition metals. The

transition metals used for this purpose may be deposited on a base layerof a different metal.

Accordingly, an object of the present invention is the provision of aliquid crystal display device having a long life.

Another object of the present invention is a liquid crystal devicewherein such gases as are evolved during operation are prevented fromimpairing the effectiveness of the device. 1

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from' the specification.

The invention accordingly comprises the features of contruction,combination of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawing, in which:

' FIG. 1 is a plan view of a liquid crystal display device ofconventional construction;

FIG. 2 is a plan view of a liquid crystal display device in accordancewith the present invention; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid crystal materialused in the preparation of liquid crystal display devices may containsmall quantities of water either as a residue from the manufacturingprocess or as the result of absorption of moisture from the air duringassembly of the device. Such water as is present will be electrolyzedwhen a sufficient voltage is impressed on the electrodes which are usedto actuate the device. As indicated above, hydrogen generated in thisway can reduce tin oxide to metallic tin thus eventually terminating theusefulness of the device. In accordance with the present invention, acatalyst, preferably metallic, is incorporated in at least one of theelectrodes to cause recombination of the gases. When H gas is adsorbedon a metallic catalyst, chemical combination between the gas and thecatalyst results. The bonds formed are covalent, as a consequence ofwhich it is desirable that the metal used as catalyst have a dorbitalgap in its electron shell. For this reason, the transition metals aresuitable catalysts. Tests have shown that platinum, palladium, nickel,rhodium, iridium and cobalt are effective for prolonging the life ofliquid crystal display devices by recombining the gases generated.

The H, generated at the negative electrode when taken up by the catalystis believed to be dissociated into active H atoms. Each atom reacts witha hydroxide ion as follows:

The oxygen molecule, in contrast, is not absorbed, but instead'acceptstwo electrons at the negative electrode as follows:

o, ,0 2e oni- OH The peroxyl ion formed in the process dissociates toform hydroxyl ion plus oxygen as shown in thefollow- The results ofcareful tests show that the recombination reaction takes place withoutany side reactions involving changes in the liquid crystal material orin the I electrodes. Furthermore, it has been found that the reactionsproceed rapidly enough so that it is not necessary to use the mosteffective catalyst such as platinum black or palladium black, which alsoare the most expensive. It is believed that the reason for theeffectiveness of the less expensive and less active catalyst metals isdue to the fact that the hydrogen and oxygen are genlating spacer 13which preferably is of plastic. Each of FIG. 3 is an exploded view inperpeetive of a segmented display device.

the sheets of glass 12 has on the inner face thereof a transparentconductive film 14. The films 14 are connected to opposite sides of a DCpower supply 15 through a switch 16 and an ammeter 17. The vesselcontains the liquid crystal material 18. Connections between theconductive films l4and the power source 15 are made by means of thevoltage leads 19. These leads also function as current leads withrespect to the faradaic current which electrolyzes the water present.

A display device in accordance with the present invention indicatedgenerally by the reference numeral 21, has one face made of glass withthe usual conductive film 14 thereon, and one face 22 consisting of acatalyst for the recombination of hydrogen and oxygen. Such a system canbe operated for long periods without degeneration.

The same objective can be achieved by making the conductive film 14 asshown in FIGS. 1 and 2 of a transition metal oxide or of oxides oftransition metal alloys. Similarly the metal electrode 22 may alsoconsist of a transition metal alloy.

To understand the severity of the problem solved by the presentinvention, it has been noted that when a field of X V/cm is imposedacross nematic liquid crystals between Nesa glasses that bubbles appearwithin an hour and that half the display area is covered with bubblesafter 2 to 3 hours. When platinum black or palladium black electrodesare used, no bubbles are generated for much longer periods.Surprisingly, when palladium plate or platinum plate electrodes having aground finish are used, bubbles similarly are not generated for a longtime. Even more surprisingly, the same effect is obtained when usingground nickel plate or materials such as rhodium, cobalt, iridium,osmium or alloys of these materials. It has also been found that theactivity of the catalyst can be adjusted by using an alloy of acatalytic transition metal and a non-active metal.

Catalytic metals and their oxides may be used in a variety of ways forthe recombination of gases generated during operation. One such form isshown in FIG. 3 where 23 is a transparent plate inscribed with indiciaand which has on one face thereof a transparent conductive layer. Theopposite face of the cell is the trans-' parent glass plate 24, theinterior face of which has thereon a segmented conductive layer, eachsegment being equipped with a conductive leadl9. In operation, voltagecan be applied to any one or any combination of the segments 26.Theresult is to change the appearance of anyone or any combination of thenumbers on the plate 23.

In another embodiment, the catalytic metal plate 22 (H0. 2) can bereplaced by a metallic base plate having thereon a facing of a catalyticmetal or catalytic metal oxide. The base plate can be of a conductivemetal and preferably of one of the transition metals which are lessactive catalysts and simultaneously less expensive than the metalsproposed for the facing layer. Such less active transition metals arenickel, aluminum, copper, manganese, chromium, iron, titanium,

of transparent metal oxides. To form such oxides, a

metal chloride or combination of metal chlorides is pits. With properdesign, such devices are also applicable where the surrounding level ofillumination is high. In addition, the attractive appearance of suchdevices makes them appropriate for use in watches, and particularly, inladies watches.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above article without departingfrom the spirit and scope of the invention, it is intended that allmatter contained in the above description and shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter ing of Pd, Pt, Ir, Rh, Co, Fe, Os, Ru and alloys thereof,

said one of said electrodes being ground to form a nonspecularlyreflecting catalyst effective for the recombination of said gases.

2. A display device as defined in claim 1, wherein the other of saidelectrodes is transparent.

3. A display device as defined in claim 1, wherein I said device hasindicia thereon, said indicia being individually susceptible to changein appearance by imposition of said voltage across said'electrodes.

4. A display device as defined in claim 3, wherein said device is aninstrument. I

5. A display device as defined in claim 3, wherein said device is awatch.

6. A display device comprising a liquid crystal material, electrodesacross which a'voltage may be applied and an insulating spacer, saidelectrodes and said spacer forming a vessel containing said material,said applied voltage serving to scatter light, said material generatinghydrogen and oxygen gases on the application of said voltage, and atleast one of said electrodes comprising a material selected from thegroup consisting of platinum black and paladium black as a catalysteffective for the recombination of said gases.

8 i t i i

2. A display device as defined in claim 1, wherein the other of saidelectrodes is transparent.
 3. A display device as defined in claim 1,wherein said device has indicia thereon, said indicia being individuallysusceptible to change in appearance by imposition of said voltage acrosssaid electrodes.
 4. A display device as defined in claim 3, wherein saiddevice is an instrument.
 5. A display device as defined in claim 3,wherein said device is a watch.
 6. A display device comprising a liquidcrystal material, electrodes across which a voltage may be applied andan insulating spacer, said electrodes and said spacer forming a vesselcontaining said material, said applied voltage serving to scatter light,said material generating hydrogen and oxygen gases on the application ofsaid voltage, and at least one of said electrodes comprising a materialselected from the group consisting of platinum black and paladium blackas a catalyst effective for the recombination of said gases.